1. Field of the Invention
The present invention relates to magnetic structures. More specifically, the invention relates to spin valve read elements that may be used in magnetic recording heads.
2. Description of the Related Art
Spin valves for reading from magnetic recording media, i.e., for sensing a magnetic field, have been used to overcome the limited sensitivity of inductive reading. A spin valve may comprise a pair of ferromagnetic layers having a nonmagnetic layer therebetween, with an antiferromagnetic layer adjacent to one of the ferromagnetic layers. The antiferromagnetic layer is a material that is generally not affected by external magnetic fields, and is therefore generally considered to be nonmagnetic. However, the material has been given a permanent magnetic orientation through exposure to magnetic fields at high temperature. The magnetization in the ferromagnetic layer closest to the antiferromagnetic layer will align itself with the magnetic field in the closest layer of the antiferromagnetic material. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the magnetic orientation within the free layer will change to correspond with this magnetic field. This relative change in the orientation of the magnetizations within the free layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve to an applied test current. Parallel magnetic orientations of the ferromagnetic layers corresponds to minimum resistance, and anti-parallel orientations of these magnetic moments corresponds to maximum resistance. A constant level of resistance, whether the minimum or maximum, indicates a binary xe2x80x9c0.xe2x80x9d A change in the level of resistance indicates a binary xe2x80x9c1.xe2x80x9d
Antiferromagnetic materials have several disadvantages when used within read elements. Most antiferromagnetic materials have poor corrosion resistance. The high temperature process used to induce antiferromagnetic properties in antiferromagnetic materials causes diffusion between the thin layers of a typical read element, thereby degrading performance. This anneal may limit the choice of materials that can be used in other parts of the head that will also be subjected to this anneal. Additionally, antiferromagnetic properties are subject to temperature, and will typically no longer effectively pin the layer of the adjacent ferromagnetic material at temperatures at or above 300xc2x0 C.
In addition, spin valves also have disadvantages that are inherent in their basic structure. For example, magnetic flux from the pinned layer, and specifically the magnetic flux from the ferromagnetic portion of the pinned layer, affects the free layer magnetic orientation. This affects the ability of the free layer to properly operate in the presence of the magnetic field that is being sensed by the spin valve and, therefore, results in a reduced effectiveness of the read element that employs a spin valve arrangement.
There is identified, therefore, a need for an improved spin valve read element that overcomes limitations, disadvantages, and/or shortcomings of known spin valve read elements. There is also identified a need for an improved magnetic structure that overcomes limitations, disadvantages, and/or shortcomings of known magnetic structures.
The present invention relates to a spin valve used, for example, for reading from magnetic recording media, wherein the antiferromagnetic layer has been replaced by a permanent magnet.
The present invention includes a recording head combining a read portion and a write portion. The write portion may be of either perpendicular or longitudinal configuration. A perpendicular recording head may include a main pole, an opposing pole magnetically coupled to the main pole, and an electrically conductive coil adjacent to the main pole. The bottom of the opposing pole may have a surface area greatly exceeding the surface area of the main pole""s tip. Likewise, a typical longitudinal recording head includes a pair of poles, with a coil adjacent to one pole. Unlike a perpendicular recording head, a longitudinal recording head may use poles having bottom surfaces with substantially equal areas. In either case, electrical current flowing through the coil creates a flux through the main pole. The direction of the flux may be reversed by reversing the direction of current flow through the coil. The opposing pole of the perpendicular head (or the first pole of the longitudinal head) can also form one of two substantially identical shields for the read elements. The shields are substantially parallel to the trackwidth, with the read element disposed between these shields. A read element of the present invention is a spin valve wherein the antiferromagnetic layer has been replaced by a permanent magnet.
One embodiment of the spin valve includes a permanent magnet, followed by a pinned ferromagnetic layer, an Ru layer, a reference ferromagnetic layer, an electroconductive layer (for example, copper) and a free ferromagnetic layer. Another preferred embodiment includes a permanent magnet, an Ru layer, a pinned ferromagnetic layer, a copper layer, and a free ferromagnetic layer. Another embodiment includes a permanent magnet, a pinned ferromagnetic layer, a Ta layer, a Ru layer, a reference ferromagnetic layer, a copper layer, and a free ferromagnetic layer. Current may be applied parallel or perpendicular to the plane for embodiments of the invention.
To read from the magnetic recording medium, the recording head is separated from the magnetic recording medium by the flying height. The magnetic recording medium is moved past the recording head so that the recording head follows the tracks of the magnetic recording medium, typically with the magnetic recording medium first passing under one shield, followed by the read element, then passing under the write portion of the recording head. As the magnetic recording medium passes under the read element, the magnetic fields within the recording medium orient the magnetic moment within the free ferromagnetic layer of the spin valve so that they are either parallel (corresponding to minimum resistance) or antiparallel (corresponding to maximum resistance), relative to the pinned ferromagnetic layer depending on the direction of the magnetic field being read from the recording medium. A sense current is passed through the GMR element by a pair of electrical contacts, thereby enabling the read element""s resistance to be detected. A constant level of resistance may be read as a binary xe2x80x9c0,xe2x80x9d and a changing resistance may be read as a binary xe2x80x9c1.xe2x80x9d
Presently available spin valves utilize, for example, an antiferromagnetic layer adjacent to a ferromagnetic layer, followed by an electroconductive layer and another ferromagnetic layer. The combination of the antiferromagnetic layer and adjacent ferromagnetic layer forms a pinned layer, although sometimes the adjacent ferromagnetic layer alone is referred to as the pinned layer. The antiferromagnetic material is one which is not generally affected by external magnetic fields, but which can be given a magnetic orientation once subjected to a magnetic field at high temperature. The adjacent ferromagnetic layer will have a magnetic orientation parallel to the orientation of the magnetic orientation in the closest layer of the antiferromagnetic layer. The ferromagnetic layer on the other side of the electroconductive material is known as the free layer, and the orientation of its magnetic moment will vary based on the magnetic fields to which it is subjected.
Antiferromagnetic materials have important disadvantages. They typically have poor corrosion resistance. They typically lose their antiferromagnetic properties at temperatures at or above 300xc2x0 C. The high temperature heating process used to induce antiferromagnetic properties can cause diffusion between the thin layers of the read elements, thereby destroying its magnetoresistive properties. The high temperature anneal also limits the choice of materials for other parts of the head that will also be subjected to this anneal. A spin valve of the present invention avoids these disadvantages by substituting a permanent magnet for the antiferromagnetic material.
In accordance with an aspect of the invention, a spin valve includes a permanent magnet layer, a reference ferromagnetic layer, and a free ferromagnetic layer. A coupling inducing layer, that provides antiferromagnetic coupling, is positioned between the permanent magnet layer and the reference ferromagnetic layer. An electroconductive layer is positioned between the free layer and the reference ferromagnetic layer. The coupling inducing layer may be formed of, for example, Ru, Rh and Cr. The electroconductive layer may be formed of, for example, Cu, Au, Ag or an alloy consisting of at least one of Cu, Au or Ag.
The spin valve may also include a pinned ferromagnetic layer positioned between the permanent magnet layer and the coupling inducing layer. In addition, the spin valve may include an epitaxy breaking layer positioned, for example, between the coupling inducing layer and the pinned ferromagnetic layer and/or an epitaxy breaking layer positioned between the coupling inducing layer and the reference ferromagnetic layer. The epitaxy breaking layer may be formed of, for example, Ta, Zr or Nb.
The spin valve may also include a seed layer positioned adjacent the permanent magnet, such that the seed layer is formed on an opposing side of the permanent magnet layer from the side on which the coupling inducing layer is positioned. The seed layer may be formed of, for example, Cr, W, TiW or MgO. The spin valve may also include a flux shunt layer and an epitaxy breaking layer positioned between the flux shunt layer and the seed layer. The flux shunt layer may be formed of, for example, NiFe, CoFe, NiCoFe or an alloy containing at least one of the elements Co, Ni or Fe.
In accordance with another aspect of the invention, a magnetic disc drive storage system includes a housing, a rotatable magnetic storage medium positioned in the housing, and a recording head mounted in the housing adjacent the rotatable magnetic storage medium. The recording head includes a spin valve wherein the spin valve may be constructed in accordance with the spin valve embodiments described herein. In addition, the spin valve may be constructed as a current perpendicular to the plane type spin valve or a current parallel to the plane type spin valve.
In accordance with yet another aspect of the invention, a current perpendicular to the plane (CPP) spin valve includes a permanent magnet layer, a pinned ferromagnetic layer adjacent the permanent magnet layer, and an antiferromagnetic coupling inducing layer adjacent the pinned ferromagnetic layer. The CPP spin valve may also include a reference ferromagnetic layer adjacent the antiferromagnetic coupling inducing layer and an electroconductive layer adjacent the reference ferromagnetic layer. A free ferromagnetic layer may be positioned adjacent the electroconductive layer. In addition, an epitaxy breaking layer may be positioned between the pinned ferromagnetic layer and the antiferromagnetic coupling inducing layer and/or between the antiferromagnetic coupling inducing layer and the reference ferromagnetic layer and/or between the permanent magnet layer and the pinned layer.
In accordance with an additional aspect of the invention, a magnetic device comprises a multilayer magnetic structure including a permanent magnet layer, a reference ferromagnetic layer, and a free ferromagnetic layer. The magnetic structure may also include a pinned ferromagnetic layer positioned between the permanent magnet layer and a coupling inducing layer. In addition, the magnetic structure may include one or more epitaxy breaking layers. The magnetic structure may be utilized in a magnetic recording head or in other applications where it may be advantageous to employ such a multilayer magnetic structure such as, for example, in a magnetoresistive random access memory device.
It is an aspect of the present invention to provide a spin valve avoiding the disadvantages of antiferromagnetic material.
It is another aspect of the present invention to provide a spin valve having a permanent magnet, a pinned ferromagnetic layer, an antiferromagnetic coupling layer, a reference ferromagnetic layer, an electroconductive layer, and a free ferromagnetic layer.
It is a further aspect of the present invention to provide a spin valve having a permanent magnet, an antiferromagnetic coupling layer, a pinned ferromagnetic layer, an electroconductive layer, and a free ferromagnetic layer.
It is another aspect of the present invention to provide a spin valve having a permanent magnet, a pinned ferromagnetic layer, a Ta layer, an antiferromagnetic coupling layer, a reference ferromagnetic layer, an electroconductive layer, and a free ferromagnetic layer.
It is a further aspect of the present invention to provide a spin valve avoiding the use of corrosive materials.
It is a further aspect of the present invention to provide a spin valve whose properties will not be compromised by high temperature.
It is another aspect of the present invention to provide a read element having a manufacturing process that does not result in diffusion of the read element""s layers.
These and other aspects of the present invention will become apparent through the following description and drawings.